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A negative pressure isolation room is intended for a patient that has active TB (or another disease transmitted by airborne means) and must be situated in a room that has a negative pressure atmosphere in relation to the area outside the room where the patient is residing. (Note: With recent developments, TB is not the only pathogen that may be of concern.) With this in mind, let's talk about what an isolation room should be. The data presented here is based on various CDC recommendations, current OSHA regulations (CPL 2.106) and JCAHO standards (EC 3.2.1-x).

The infectious isolation room is a regulated room. It is regulated by the Occupational Health and Safety Administration (OSHA) and must meet additional standards of JCAHO. If you are an "acute care facility", you MUST have at least one negative pressure isolation room. The regulations by that body are intended to protect the Health Care Workers (HCW) from exposure to TB and other airborne pathogens. Dependent on State code your governmental health department may have additional jurisdiction over standards for isolation rooms.

can reduce the overall risk of infection in a room in two ways: dilution and removal. When clean air is supplied to a room, it dilutes the concentration of airborne contaminants in the room. Dilution reduces the likelihood that a person in the room will breathe air that may contain contaminants. In the case of M.Tb, this effect means that a person will be less likely to inhale one or more droplet nuclei.

The removal effect occurs when air from a room is either:

•  discharged outdoors or to a safe place,
•  or, passed through a HEPA filter to trap droplet nuclei before recirculation.

The amount of ventilation in an isolation room is usually expressed in Air Changes per Hour (ACH). By calculating the air change rate, the room ventilation can be compared to published standards, codes, and recommendations. It can also be used to estimate the length of time required for removal of infectious particles.

One air change occurs in a room when a volume of air equal to the volume of the room is supplied and/or exhausted. The air change rate, in ACH, is the volume of air circulating every hour divided by the room volume.

The current JCAHO standard for negative pressure infectious isolation rooms is twelve (12) ACH minimum, with fifteen (15) ACH preferred. This air change rate may be different for other "critical areas" in the healthcare facility. See the section entitled "AirSecurity™ for Other Areas". Beginning January 1, 2003, "critical areas" are not grandfathered and must be brought up to the new standard in a timely manner.

A ventilation system introduces and removes air by means of air outlets. In health-care applications, outlets are usually mounted on a ceiling or on a wall. Ceiling supply outlets are called diffusers. Wall supply outlets are called grilles or registers. Exhaust (or return) outlets are also called grilles or registers, regardless of whether they are mounted on the ceiling or the wall.

Ventilation air supplied to a room by a mechanical system will mix with air already in the room. This air mixture is removed by exhausting via the HVAC return system or preferably by individual air purification systems (APS). The effectiveness of dilution and removal depends on the effectiveness of the mixing process: the better the mixing, the better the dilution and removal. Stagnation and short-circuiting need to be avoided.

The exhaust grille, in contrast to the supply diffuser/register, is a passive device; it simply gathers air that is near. To encourage air mixing, the exhaust grille should be located at a point remote

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from the supply and as near to the patient’s head as possible. The grille should have a neck sufficiently large to easily draw in the required exhaust air quantity.

Ventilation can also reduce the local concentration of infectious particles at certain locations in a room. This is achieved by coordinating the location of the ventilation outlets with the probable positions of the patient in the room. Simply stated, supply air should be introduced near staff entrance, and exhaust air should be collected near patient’s head. The efficiency of this air dynamic can be confirmed by particle degradation and regression analysis.

Negative pressure is created by setting (or balancing) a ventilation system so that more air is mechanically exhausted from a room than is mechanically supplied. This creates a ventilation imbalance, called an offset. The room makes up the offset by continually drawing in make-up air from outside the room.

A negative pressure room must be as airtight as possible to prevent air from being pulled in through cracks and other gaps. This is called sealing a room. In a sealed room, the direction from which the make-up air enters the room and the speed with which it moves can be controlled. The smaller the make-up air opening, the faster the make-up air will move.

HEPA Filters are generally constructed of a 0.013 inch thick glass fiber material that is bonded at the molecular level. Required minimum HEPA standards include 99.97% capture of 0.3 micrometer diameter DOP aerosol particles. A True HEPA's DOP rated efficiency (which is 99.97%) is the MINIMUM STARTING efficiency. The actual operating efficiency is higher for all particle sizes (0.001 micron and up).

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HEPA APS filter motor/blower systems are readily available electrical devices that consist primarily of a fan, a HEPA filter, and a prefilter. They also include controls, such as a three-speed switch, and possibly an indicator light to indicate when the filter needs to be changed. HEPA filter units are available in a number of different physical configurations, including portable, in-ceiling, in-duct, and external weatherized roof mounted types.

Ceiling-mounted units are less obtrusive and do not take up floor space. They are also less likely to be tampered with by staff and patients. However, floor mounted units are more portable and are easier to service. Regulatory bodies, such as OSHPD in California, may require that a structural engineer oversee the design and construction of the support system for a ceiling mounted HEPA filter unit.

The size of the unit selected should be based on the additional airflow (in CFM) required to achieve the desired air change rate (in ACH) in your room. To determine the additional airflow:

2. Calculate the CFM required to achieve the desired ACH. The HEPA filter unit should be sized to make up the difference.

Ultraviolet Germicidal Irradiation (UVGI) is a secondary method of removing airborne pathogens from the air stream. It cannot be used in place of HEPA filtration. It may be added as an adjunct to HEPA filtration.

Provided that the UVGI is specified correctly, this extra measure can ensure that ALL pathogenic material is eradicated as it is collected on the HEPA filter. MAS quotes most air purification equipment with this option installed. It is important to keep in mind that UVGI is NOT a substitute for HEPA filters. UVGI offers a second line of defense against airborne pathogens but all (OSHA, JCAHO, CDC, NIOSH, etc) agencies consider the HEPA filter as the primary defense against airborne pathogens.

When used in an isolation room, UVGI can lower the concentration of infectious particles. In fact a recently published NIOSH study in conjunction with the University of Colorado and Harvard Medical School has proven indirect UVGI will offer the equivalency of 33 additional ACH in an Isolation room so engineered ("Public Health Records", March-April, 2003, volume 118, pp 99-114)

Because direct exposure of UVGI can have negative short-term health effects on the skin and eyes, a safety plan should be implemented if and when it is used. The indirect UVGI method is preferred by NIOSH as a method of enhancing the air sterility in an isolation room. For air purification UVGI has basically three applications: in-duct UVGI, on coils UVGI and upper room atmosphere air UVGI.

A continuous monitoring device is required for all negative pressure isolation rooms by JCAHO as of 1/1/03. All infectious isolation rooms, including surgical suites, MUST have a continuous monitoring devices installed for each room. The new requirements state that the rooms be monitored 24/7. They must also locally alarm both audibly and visually so that personnel can become immediately aware of and correct any problems that may occur. Some more advanced room pressure monitors have the ability to directly interface with building automation systems, (BAS).

There are other areas of healthcare institutions that the AIA and JCAHO have designated as "critical areas". The partial list below is then standards that were implemented on January 1, 2003. The "Air Movement" category states either "In", "Out" or there is no response. "In" signifies a negative pressure area while "Out" signifies a positive pressure area.

MAS has had personal communication with Mr. Kurt A. Pratton, Executive Director of Hospital Accreditation Services with JCAHO who stated that these standards were effective on January 1, 2003 and that these critical areas will not be "grandfathered".

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